1. Field of the Invention
The present invention relates to a novel structure of a small ship, in particular, to a construction of a small ship able to be built from prefabricated units. The term small ship as used in this specification refers to ships used mainly for leisure activities or sightseeing, or to small fishing boats.
2. Description of the Related Art
The construction of small ships is divided roughly into two types, as explained hereinbelow.
In the first type of construction, a shape of the ship is molded from a plastic material and allowed to solidify. Then the molded plastic shape is laminated with a reinforcing material, such as a glass fiber, whereby the shell of the ship is obtained. The shell is then usually strengthened, from the inside, by strengthening members such as a keel, cross members, and bulkheads.
In the second type of construction, a skeletal structure such as a keel and cross members is first fixed together, and the shell is then fixed to the skeletal structure. Plates of, for example, wood, steel or aluminum are used as the shell. An example of this type of construction is a ship built by a strip-planking method. The first type of construction is widely used, since mass production becomes possible once a mold is made. Nevertheless, this method has a drawback in that much labor is required for the curing of the plastic material to obtain a laminated reinforced material, using, for example, glass fibers, and this drawback is accompanied by a difficulty in maintaining good working environmental conditions. Furthermore, the thus-built ship body will last long after the service life of the ship is exhausted, and it is difficult to dispose of the body, thus causing a drawback in that it cannot be recycled.
Furthermore, if the size of the ship body is increased, the making of the mold becomes complicated, and thus a reduction of a manufacturing cost cannot be obtained unless mass production is possible.
The second type of construction provides less freedom with regard to the shape of the ship which can be built, because the shell is fixed to the prefabricated skeletal structure. From the viewpoint of maintenance, an aluminum ship is advantageous, but a problem arises in that the building costs are high in comparison with those of the FRP ship, when the prior construction type is employed. In the case of the aluminum ship, in particular, an enormous affect is exerted by a distortion generated when welding is done, whereby the number of working units must be increased to eliminate the distortion.
Both of types of construction must be used in coastal zones when the ship, even if small, is of a size that makes overland transportation difficult (a ship having a length of more than 2.5 meters is very difficult to transport overland), and thus the number of shipbuilding sites is limited, and sometimes there is insufficient manpower available at the site.